1. Field of the Invention
This invention relates generally to magnetic type digital storage apparatus and more particularly to circuitry for actively damping overshoot in the writer output current waveform of a hard disk drive read/write head controller integrated circuit.
2. Description of Related Art
Conventional hard disk drives currently being manufactured typically utilize an analog integrated circuit (IC) chip known as a read/write head controller, also referred to as a xe2x80x9cpreampxe2x80x9d. The purpose of the preamp is to provide an interface between the read channel and the read and write heads. The preamp includes a write driver portion which provides a bipolar square wave of current to the inductive write head. The head current must be of a programmable magnitude as well as being well controlled. The changing polarity of the write current waveform writes a logic xe2x80x9c1xe2x80x9d to the spinning magnetic disk of the hard drive. The inductive write head, in combination with the accompanying interconnection wiring and preamp, forms a complex resistive, inductive, capacitive (RLC) circuit which in turn introduces a certain amount of ringing or overshoot in the preamp output current waveform as shown in FIG. 1. In the past, this overshoot has been damped to some degree by simply shunting the write driver output with a resistor. More recently, disk drive manufacturers have required of preamp suppliers the ability to precisely control the amount of overshoot and to be able to vary the overshoot after the drive has been assembled.
Previous schemes for providing controlled damping of the write driver output current waveform has been to utilize various sized damping resistors selectively coupled across the write driver output. However, the damping resistors typically require large transistors, such as field effect transistors, (FETs) connected to the output to switch the resistors in and out of the write driver output circuit. This has resulted in unwanted parasitic capacitance on the output which limits writer speed performance and the number of damping levels practically integrated. In addition, because of the process and temperature variation associated with integrated circuit components, i.e., the resistors, the amount of damping could not be adequately controlled.
Accordingly, it is an object of the present invention to provide an improvement in magnetic memory apparatus.
It is another object of the invention to provide an improvement in the control of the write current supplied to a write head of a magnetic memory.
It is still another object of the invention to provide an improvement in the control of overshoot in the write driver current waveform from a read/write head controller used in connection with hard disk drives.
It is still yet another object of the invention to provide programmable active damping of the write driver output current waveform from a read/write head controller used in connection with hard disk drives.
These and other objects of the invention are achieved by controlled damping of the write driver output current prior to the write driver output stage, thus minimizing output parasitics and configured in such a way that it becomes process and temperature insensitive. In the present invention, overshoot damping is provided by a combination of passive damping and active damping so as to provide a minimum base level of damping while additionally providing a programmable damping feature. Passive damping is provided by shunting a resistor across the write driver output terminals, while active damping is provided by sinking, i.e., subtracting, a precise amount of current, for a predetermined duration, at the beginning of each transition of a bipolar write driver output current fed to the write head of a hard disk drive.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and the specific example, while indicating the preferred embodiment of the invention, is provided by way of illustration only, since various changes, alterations and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.